1. Field of the Invention
This invention relates to a training or exercising system and method.
2. Background Art
Traditional weight lifting involves selecting a fixed amount of weight to be lifted and lowered through a user's range-of-motion (ROM). This means that a constant resistance level or “load” is applied to the muscles throughout the ROM in both directions. Once the load has been selected, the user controls the velocity of each lift along with the number of repetitions to be performed.
Typical resistance training equipment utilizes a cable- and pulley-driven weight stack that works against gravity and is manipulated by a user interface. The user typically selects a fixed amount of weight to be lifted by inserting a pin at the appropriate place in the weight stack. The weight is then lifted and lowered through the user's ROM through the application of force to the user interface and the transfer of that force through the cable and pulley mechanism to the weight stack. Such “weight machines” are widespread in health clubs, physical therapy clinics, and home gyms.
Muscle mass and strength tend to increase in response to the force stimulus of a load being applied to the muscle. The greater the force (without causing injury), the greater is the training stimulus. Thus, training with weights that are a significant percentage of an individual's maximum capability tends to produce the greatest increases in strength.
For any joint in the human body, the relationship between force generation capacity and joint angle is non-constant and non-linear. That is, the maximum amount of weight that can be lifted for a given exercise varies at each position along the ROM. For example, in performing a leg press repetition, a person is substantially weaker in the position where the knees are flexed than where they are more fully extended. In fact, this strength difference may be as great as a factor of three or more. Thus, when performing a single repetition on a traditional weight machine, which can only apply a constant load, the user is restricted to selecting a weight no greater than that which can be lifted at the weakest position within the ROM. This means that with traditional weight lifting, the user is “under-training” throughout most of the ROM in that he receives a smaller training stimulus in the stronger regions.
The force generation capacity also varies with the “direction” of training (FIG. 1). When a muscle contracts, it attempts to shorten and generates tension. If this tension exceeds the externally applied load, a shortening contraction (SC) will occur and the muscle length will shorten (velocity>0 m/s). For example, when one lifts a weight or ascends the stairs, the agonist muscles undergo an SC whereby the muscle fibers contract and shorten while moving and performing work on the weight. If the external load exceeds the tension generated by the contracting muscle, the muscle will be stretched and is said to undergo a lengthening contraction (LC) (velocity<0 m/s). For example, when the weight is lowered or the stairs are descended, the muscle fibers actually lengthen as they contract and the weight performs work on them, resulting in an LC. Isometric contractions occur when a muscle develops tension but the muscle length does not change (velocity=0 m/s). Skeletal muscle routinely performs shortening, isometric, and lengthening contractions in normal daily activities.
As illustrated in FIG. 1, muscle can generate significantly greater force during lengthening contractions as compared with isometric or shortening contractions. More particularly, muscle tends to be anywhere from 1.5 to 3 times stronger in the LC phase of a lift than in the SC phase. This means that one can actually control the lowering of much more weight than can be lifted. This lengthening contraction overloading capacity can be exploited to evoke greater increases in muscle mass, strength, and power. In traditional weight training, the muscles are substantially “under-loaded” in the LC phase of the lift since the load can be no greater than the amount of weight that can be lifted in the weakest position of the weaker SC phase.
LC training has been shown to provide significant benefits, including greater strength gains and improved protection from injury, all at lower levels of perceived exertion, cardiovascular stress, and oxygen consumption, and is important for activities such as downhill skiing, tennis, basketball, downhill hiking, stair descent, and others. Once more, since traditional weight machines limit the user to selecting a single fixed weight that must be lifted and lowered through the entire ROM, the muscles are under-trained during the LC phase of training. Serious athletes often try to reduce the magnitude of under-training by selecting a weight greater than they are capable of lifting. A training partner is employed to assist with the lift and then lets the user lower the weight himself to get a better loading effect in the LC phase. This type of training, often referred to as “negatives”, is not generally available to casual weight lifters, the elderly, or those who train by themselves.
Gains in muscle strength tend to be specific to the type of training performed. Thus, SC training evokes greater increases in SC strength than LC training, while LC training leads to greater LC strength gains than SC training. Since everyday activities require both SC and LC movements, the American College of Sports Medicine and others recommend a strength training regimen utilizing both types of movements. Moreover, numerous training studies have demonstrated that regimens involving both SC and LC training produce the greatest increases in dynamic muscle strength and change in morphology. Also, acute hormonal responses are associated with specific SC or LC training movements. But, as described above, traditional fixed-weight training under-emphasizes the LC phase of training, while recently developed systems that focus entirely on the LC phase of training, by design, omit training the SC phase. Despite the advantages and need for such a regimen, no system exists that has the flexibility to enable both lower-load SC and higher-load LC training that is suitable for independent use.